unstable$ echo "a A a A" | grep -o a
a
a
unstable$ echo "a A a A" | grep -io a
a
A
a
A
unstable$ echo "a A a A" | grep -o "[aA]"
a
A
a
A
unstable$ echo "a A a A" | LC_ALL="en_US.utf8" grep -io a
a
A
a
A

CVS version: compiled from CVS and installed in $HOME.

unstable$ echo "a A a A" | ~/bin/grep -o a
a
a
unstable$ echo "a A a A" | ~/bin/grep -io a
a
A
a
A
unstable$ echo "a A a A" | ~/bin/grep -o "[aA]"
a
A
a
A
unstable$ echo "a A a A" | LC_ALL="en_US.utf8" ~/bin/grep -io a
a
A
a
A

Great to see the fast and accurate response - it's what i expect from GNU. :)

> CONCLUSION: The bug affects not only highlighting,
> but also the --only-matching option.

This seems to be fixed in CVS. At least, I cannot reproduce your results with grep from CVS, nor on Ubuntu Edgy, nor on a current Gentoo installation. Your Knoppix is somewhat old; please retry with a later version.

This is my first time posting, so I hope no one has already posted this. I'm using grep 2.5 on windows XP.

When I run grep with the -i option the match color does not display. Please note that with or without the -i command, I always see the same grep output when my regexp is "someInst"...the problem here is the color highlight match.